Hydrocarbon reform process



Jan. 1, 1963 G. R. JAMES 3,071,453

HYDROCARBON REFORM PROCESS Filed Jan. 12, 1960 GEORGE RUSSELL JAMESINVENTOR.

BYQZYL- AGENT 3,071,453 Patented Jan. 1, 1963 ical QonstructionCorporation, New York, N.Y., a corporatron of Delaware Filed Jan. 12,1%0, Ser. No. 2,004 2 Claims. (Cl. 48-196) This invention relates to aprocess of catalytic hydrocarbon reform, in which a hydrocarbon streamis reacted with steam at elevated temperature to produce a gas streamknown as synthesis gas which is subsequently util1zed in variousprocesses. In the present invention the heat content of the synthesisgas is utilized to provide power to compress the gas prior to usage inhigh pressure processes such as ammonia or methanol synthesis.

The reforming of hydrocarbons is a well-known procedure, in which ahydrocarbon raw material is reacted with steam to produce a mixed carbonmonoxide-hydrogen gas stream. Probably the hydrocarbon raw material mostcommonly used in this process is methane, which is the principalconstituent of natural gas and is a major constituent of other gaseoushydrocarbon streams such as refinery off-gases. Of course, otherhydrocarbon gases or liquids are also reformed in this manner. Theconventional process comprises mixing the gaseous hydrocarbon streamwith steam, and passing the mixed gas stream through the catalyst tubesof an externally-fired reformer uni-t. Under the elevated temperaturecondition and in the presence of the catalytic material, the hydrocarbonwill react with the steam to yield a mixed carbon monoxide-hydrogenreformed gas stream.

In the case of ammonia synthesis, the reformed gas stream is furthercatalytically converted in a carbon mon oxide oxidation unit, usuallywith the addition of further steam. In this process the carbon monoxidereacts with water vapor to yield further hydrogen and also carbondioxide. The carbon dioxide is then removed, usually by scrubbing withaqueous potassium carbonate or monoethanolamine solution. The residualgas stream, consisting principally of hydrogen, is then thoroughlypurified by known procedures and mixed with nitrogen. The mixed gasstream is thereafter compressed to ammonia synthesis pressure which isusually .above 4000 p.s.i.g. and passed to the ammonia synthesis unit.

Another commercial usage for reformed gas is in methanol synthesis. Herethe carbon monoxide content of the reformer gas may be only partiallyconverted to carbon dioxide and hydrogen, with subsequent carbon dioxideremoval. In methanol synthesis the feed gas to the methanol convertershould have a hydrogen to carbon monoxide mol ratio of 2:1, hence insome cases the CO- oxidation step will not be required. The methanolconverter feed gas is compressed to about 5200 p.-s.i.g. prior tocatalytic conversion to methanol.

Among other reformer gas utilizations which require preliminary gasprocesing similar to the ammonia procedure, may be mentioned catalytichydrogenations such as are practiced in the petroleum and vegetable oilsrefining industries. These processes are also usually carried out at anelevated pressure.

In these various processes the final gas stream is cooled prior tocompression since this is required for thermodynamic efficiency in thecompression step. The excess heat is usually removed by means of a heatexchanger utilizing cooling water which is usually subsequently passedto a cooling tower and recirculated to the heat exchanger. Thus theundesirable heat content of the gas stream has been wasted, since thisheat is available at a relatively low level which has heretoforeprecluded utilization except in gas-to-gas heat exchangers within theprocess itself as described in U.S. Patent No. 2,487,981.

In the present invention, the hot reformer gas is cooled in a boiler orother means whereby the heat which is removed from the gas serves togenerate steam at a re-. latively low pressure. The cooled gas, aftervarious purification steps as indicated above, is then compressed bymechanical means. The previously generated steam is utilized in a steamturbine which serves to drive the gas compression unit which in turn isused to compress the gas. This improved process results in higherthermal efiiciency and complete utilization of energy which hadheretofore been wasted.

An object of the present invention is to produce a gas stream containinghydrogen at elevated pressure from hydrocarbon raw material in a moreelficient manner.

Another object of this invention is to more completely utilize thethermal energy available in hot reformer gas;

A further object of this invention is to compress a synthesis gasderived from hydrocarbon reforming without consuming power derived fromexternal sources for the compression.

An additional object of this invention is to provide a novel combinationprocess for producing hydrogen-com taining gas at elevated pressure withreduced energy requirements.

These and other objects of the present invention will become apparentfrom the description which follows. Referring to the FIGURE, whichrepresents a preferred embodiment of the present invention, stream 1 isan input natural gas stream, principally methane.- A' portion of stream1 is utilized for the reforming process, and passes via lines 2 and 3into catalyst tube 4 of reformer 5. Stream 3 consists of natural gasmixed with the proper proportion of steam, admitted via 6. A portion ofstream 1 may be utilized via line 7 for the external firing in reformer5. In this case stream 7 is burned with air admitted via 8 to providethe heat and proper temperature level for the reforming reaction withintube 4. Usually a temperature of 1000 F.1800' F. is required in unit 5to produce the required reform temperature of 600 F. to 1500 F. withintube 4. It should be recognized that stream.7 is optional, othercombustible gas streams or thermal sources may be employed for externalfiring in reformer 5. Flue gases derived from the com bustion of stream7 pass to a stack via 9.

Catalyst layer or bed 10 is provided within tube 4 of reformer '5. Asthe mixed stream 3 containing steam and hydrocarbon such as methanepasses through tube 4,,a catalytic reaction takes place between themethane or other hydrocarbon and stream resulting in the formation ofcarbon monoxide and hydrogen. The resulting product gas stream 11 leavesreformer 5 at an elevated temperature, usually about 800 vF. to 1000 F.and is cooled in steam generation means 12. Unit 12 is preferably asteam boiler, with condensate water passed in via 13 and generated steamleaving via 14. Unit 12 is preferably operated so as to maintain a steampressure between 25 p.s.i.g. and p.s.i.g. in line 14, since thisproduces optimum heat recovery from line 11. A conventional waste heatboiler, not shown, may be used to partially cool stream 11 and recoverhigh pressure steam prior to passing stream 11 through unit 12.

The cooled product gas stream leaves unit 12 via 15 and may be furthercooled prior to compression in a conventional heat exchanger unit, notshown. Stream 15 is then compressed to proper elevated pressure incompression means 16. Uni-t 16- is a suitable centrifugal orreciprocating gas compressor, powered by shaft 17. The product gasstream, now at elevated pressure, is passed to synthesis gas utilizationvia 18. As previously decribed, line 18 may transmit the gas to avariety of processes among which may be mentioned methanol synthesis andpetroleum refining.

Returning to steam boiler 12, the generated steam, line 14, passes firstthrough optional heater unit 19 which may serve to super-heat the steam.The steam in any case now passes via line 20 through steam turbine 21.Depending on operating variables, it may be desirable to pass additionalsteam from other sources through turbine 21 via line 22. However, it israrely necessary to furnish more than about of total power requirementin this manner. The steam feed from lines and 22 drives turbine 21 whichin turn transmits power through shaft 17 into gas compressor 16. Theexhaust steam leaves turbine 21 via 23 and is condensed in cooler 24 andrecycled via 13 as liquid condensate water. Cooler 24 uses cooling wateradmitted via 25 and exiting via 26 to condense exhaust steam in line 23.

In a modification of the present invention, a portion or all of thecarbon monoxide in the hot reformer exit gas stream 11 may becatalytically reacted with water vapor to provide further hydrogen andcarbon dioxide in a shift converter, not shown. A unit of this type isdescribed in US. patent application No. 760,187, filed September 10,1958. This procedure would be used when the final gas stream is to beprincipally hydrogen, as in ammonia synthesis and catalytic organichydrogenations. In this case the cooled gas stream 15 following unit 12would first be treated to remove carbon dioxide as in a scrubbing tower,not shown, prior to compression. A partial carbon monoxide conversion toprovide the proper carbon monoxide-hydrogen ratio might also be providedin the case of product gas usage for methanol synthesis.

Industrial applications of the present invention will now be described.

Example I A stream of natural gas was utilized to produce a highpressure reformed gas product. The natural gas consisted mostly ofmethane, and in the following description all flow quantities are per100 mols methane reformed. Thus per 100 mols methane reformed, 167 molsof natural gas were consumed. The natural gas was obtained at 275p.s.i.g., and was first scrubbed with monoethanolamine (MEA) solution,which removed 6.7 mols of hydrogen sulfide from the gas stream.

The purified gas stream was then split, with 100 mols passing tocatalytic reform together with 560 mols of steam derived from waste heatboilers at 275 p.s.i.g. The balance of the natural gas was used forheating purposes, mainly for external firing of the reformer furnace andpreheating of the natural gas prior to reform. The reformed gas streamwas produced at 1400 F. and 240 p.s.i.g., and was first cooled to 712 F.in a waste heat boiler. The generated stream was utilized as a portionof the steam added to further incoming natural gas prior to reform. Thebalance of this steam was obtained from a second waste heat boiler,which obtained heat from the reformer furnace flue gases.

The partially cooled reformed gas stream was now further cooled to 267F. in two stages of low pressure steam generation. The first stageproduced 3800 pounds of steam at 70 p.s.i.g. and cooled the gas streamto 341 F. at 235 p.s.i.g., while the second stage produced 3350 poundsof steam at 15 p.s.i.g. while cooling the gas to 267 F. at 232 p.s.i.g.The gas stream was then utilized as a heat source in the reboiler of theMEA regenerator and 'for boiler feed water preheat, and was finallycooled to 100 F. at 220 p.s.i.g. using a conventional gas cooler.

The cooled gas was then compressed to 600 p.s.i.g. in a centrifugalcompression system. The centrifugal compressor was driven by a steamturbine which utilized the 70 p.s.i.g. and 15 p.s.i.g. steam previouslygenerated for motive power. After expansion in the steam turbine, theexhaust steam was condensed to liquid water condensate at 150 F. andrecycled.

Example II Ammonia synthesis gas was produced by reforming natural gas,with compression prior to catalytic ammonia synthesis being accomplishedin accordance with the teachings of the present invention. In order tominimize compression requirements, reforming of the natural gas wascarried out at relatively high pressure.

Natural gas input to reforming was 1450 mols/hour, with steam added toprovide a mixed stream with a 5.621 ratio of steam to natural gas. Themixed stream was heated to 500 F. by heat exchange with hot productammonia synthesis gas, and then to 750 F. by heat exchange with hotreformed gas in CO-oxidation interbed cooler. Gas stream pressure was600 p.s.i.g. The mixed stream then passed to primary catalytic reform,which took place in externally-fired reform tubes. The partiallyreformed gas was essentially completely converted in a secondary reformstep, during which 1900 mols/hour of air was added to the gas stream.

The fully reformed gas stream was cooled from a secondary reform exittemperature of 1450 F. to 800 F. in a waste heat boiler. Product steamfrom this boiler, together with steam derived from a flue gas waste heatboiler which utilized the primary reformer flue gases as a heat source,comprised the reform steam which was mixed with incoming natural gas.The reformed gas stream, now consisting mostly of hydrogen, nitrogen,carbon monoxide, carbon dioxide and water vapor, was then passed througha two-bed catalytic CO oxidation unit, in which interbed cooling of thegas stream from 825 F. to 575 F. was carried out by the aforementionedheat exchange with the incoming mixed stream of natural gas and steam.The product gas stream, consisting mainly of hydrogen, nitrogen andcarbon dioxide, was also cooled from 580 F. to 400 F. by heat exchangewith the incoming mixed stream of natural gas and steam.

The gas stream, now at 530 p.s.i.g., was completely cooled from 400 F.to 230 F. in three stages using waste heat boilers, with final steamgeneration at 15 p.s.i.g. The steam generated in this manner wassuperheated and expanded in a steam turbine drive which powered theammonia synthesis gas compressor. Only 10% of the total energy wasderived from the superheat step, in other words, of the energyrequirement for compression was derived from the heat recovered from thegas stream in the form of low-pressure steam.

The fully cooled gas stream was scrubbed free of carbon dioxide in aconventional hot potassium carbonate scrubbingsystem, and finalpurification by copper liquor scrub yielded a product ammonia synthesisgas consisting of nitrogen and hydrogen at 500 p.s.i.g. with 0.2% argonand 1.0% methane inert impurities. This gas stream was compressed to5200 p.s.i.g. in the aforementioned ammonia synthesis gas compressor,and passed to catalytic ammonia synthesis.

The above descriptions of specific embodiments should not be construedto limit the scope of the teaching of the present invention, since othermodifications within the scope of the present invention will occur tothose skilled in the art.

I claim:

1. Process for generating a high pressure synthesis gas streamcontaining hydrogen which comprises catalytically reacting methane withsteam at a temperature between 600 F. to 1500 F. to produce a reformed'gas stream principally comprising carbon monoxide and hydrogen,partially cooling said reformed gas stream to a lower temperature above350 F. by heat exchange with water whereby high pressure process steamis produced, further cooling said reformed gas stream by heat exchangewith water whereby low pressure steam is produced at a pressure between25 p.s.i.g. to p.s.i.g., compressing said cooled gaseous stream inmechanical compression means, and expanding said low pressure steamthrough power producing means connected to said compression means,whereby said low pressure steam provides at least a portion or" thepower requirement of said compression means.

2. Process of claim 1, in which the carbon monoxide in said reformed gasstream is at least partially reacted with additional steam in a furthercatalytic step to produce further hydrogen and carbon dioxide prior tosaid further cooling step, and resulting carbon dioxide contained inReferences Qited in the file of this patent UNITED STATES PATENTS Younget a1. Apr. 18, 1933 De Jahn Aug. 28, 1945 Hagy Jan 3, 1950 Shields June28, 1960

1. PROCESS FOR GENERATING A HIGH PRESSURE SYNTHESIS GAS STREAMCONTAINING HYDROGEN WHICH COMPRISES CATALYTICALLY REACTING METHANE WITHSTEAM AT A TEMPERATURE BETWEEN 600*F. TO 1500*F. TO PRODUCE A REFORMEDGAS STREAM PRINCIPALLY COMPRISING CARBON MONOXIDE AND HYDROGEN,PARTIALLY COOLING SAID REFORMED GAS STREAM TO A LOWER TEMPERATURE ABOVE350*F. BY HEAT EXCHANGE WITH WATER WHEREBY HIGH PRESSURE PROCESS STEAMIS PRODUCED, FURTHER COOLING SAID REFORMED GAS STREAM BY HEAT EXCHANGEWITH WATER WHEREBY LOW PRESSURE STEAM IS PRODUCED AT A